Sail drive anode

[Sootydog]

Hi,
   Just dived under the boat and noticed that the whole saildrive anode is missing.  How much of a problem is this?  I dont fully understand the electrical details or how it has dropped off (im sure it was there at the beginning of the season - honest) but I was intending to be connected to shore power for a couple of days whilst we winterise before lift out.  The anode bolted to the hull forward of the saildrive is intact.

                            Thanks.

[Symphony]

The anode on the saildrive is important for obvious reasons. However a couple of days before you get lifted is not really an issue, neither is being connected to shorepower. The saildrive is electrically isolated from the boat's electrical systems. The hull anode is also unconnected with the saildrive - literally.

You don't say what model saildrive you have, but in either case it is very unusual to disappear completely. In the older type the screws holding it on are behind the prop so even if they come loose the anode cant fall off. On the later type with a split anode it is difficult to imagine how the two screws could come undone if they ere properly installed.

[Sootydog]

Symphony,  its a 130S-B. & I think I can see both fixing holes.  There is a fair bit of tube worm activity on the exposed metal so now I'm beginning to wonder how long it has been like that. She has been in the water since May and stationary for 6 weeks in the marina with no shore power attached. Could I have been subjected to a lot of stray mains current or am I just unlucky. Anything specific I can look for regarding damage once she is lifted?
      Thanks

[Salty]

Symphony,  its a 130S-B. & I think I can see both fixing holes.  There is a fair bit of tube worm activity on the exposed metal so now I'm beginning to wonder how long it has been like that. She has been in the water since May and stationary for 6 weeks in the marina with no shore power attached. Could I have been subjected to a lot of stray mains current or am I just unlucky. Anything specific I can look for regarding damage once she is lifted?
      Thanks

Yes, check very carefully for any erosion of your aluminium saildrive leg. If your anode has eroded away, then either there is some incorrect connection of electrical systems onboard to your saildrive leg, or your marina has a faulty electrical system. Either way I’d want a new anode on A.S.A.P., and an immediate investigation into why your anode from the beginning of the season has disappeared, though you don’t seem entirely sure whether it was actually in place at the start of the season?

If erosion was the cause of the loss of anode, be aware that your aluminium saildrive leg is likely to be the next part to disappear. That can be very painful in the pocket.
I have recently changed from an aluminium to a bronze propeller, and my anode has been eaten away much more than before, though obviously not as badly as yours as it’s shape remains recognisable, but it will have to be renewed before next launching.

[Yngmar]

It's a common problem that the fixing points (around bolts) on anodes erode away and then the whole thing falls off. To prevent this, apply some waterproof grease to the bolt heads (not threads) and the anode around the fixing holes. This will not prevent electrical contact, but will prevent seawater getting to those surfaces and thus avoid eroding these small, but important areas.

You should also apply Loctite threadlocker to the anode bolt threads to prevent them from vibrating out.

Few boatyards will do either of those things due to not giving a damn and usually being in a hurry, but anode changes are an easy job that every owner can and should do themselves. Only then you can be sure it's done correctly.

If there is fouling in the area where the anode was, it probably fell off some time ago. Inspect the saildrive housing for pitting when you're out of the water, especially any areas where the paint is missing.

[Sootydog]

  Yngmar,

Please excuse my ignorance on this subject, but what does the anode bolted to the hull do?

 If i find pitting, how thick is the housing?  Or in other words how deep does the pitting need to be before i get a large expense?  At the moment the oil looks OK (no sign of milkyness).

Can the pitting be filled with a suitable metal filler / glue?  Should the leg be sanded, primed and re-painted?

Loads of questions (as usual)

 Thanks

[Yngmar]

Please excuse my ignorance on this subject, but what does the anode bolted to the hull do?

 If i find pitting, how thick is the housing?  Or in other words how deep does the pitting need to be before i get a large expense?  At the moment the oil looks OK (no sign of milkyness).

Can the pitting be filled with a suitable metal filler / glue?  Should the leg be sanded, primed and re-painted?

What the hull anode does depends entirely on what it is connected to. So just look inside the boat where the wires from the hull anode bolts go to. Our boat, being a fully isolated one does not have or need a hull anode.

Don't know how thick the housing is, maybe 3-4mm I would guess, varies where. Yes, if you can find pitting, you can fill it, after cleaning it up. I used International Watertite to fill some pitting on our (also aluminium) lower rudder bearing housing and the leftovers to fair the lead keel and fix up the windlass body. Held up superbly in all three cases, so I guess that's a recommendation.

If there is any paint missing off the leg, it's definitely worth touching that up or repainting if it's widespread or you had to fill in pitting. The paint layers isolate the metal from the seawater entirely, which greatly reduces galvanic corrosion and therefore makes your anode(s) last much longer. Ours last two years and have plenty left when we replace them.

[Symphony]

  Yngmar,

Please excuse my ignorance on this subject, but what does the anode bolted to the hull do?

 If i find pitting, how thick is the housing?  Or in other words how deep does the pitting need to be before i get a large expense?  At the moment the oil looks OK (no sign of milkyness).

Can the pitting be filled with a suitable metal filler / glue?  Should the leg be sanded, primed and re-painted?

Loads of questions (as usual)

 Thanks

As I suggested it is highly unlikely that the anode has eroded in that time to the point that it fell off. Also surprising if the screws came undone without you being aware of it. As you know the anode is very different from the 120 type in Yngmar's photos and does not have that thin landing point for the screws. It is also over twice the weight of the 120 type. My 130 is still on its original anode after over 3 years in the water. It is just over 50% worn (checked in July) and will be replaced this winter.

If you have the button anode on a stud through the hull on the centre line I believe it is bonded to the DC circuit but don't think it protects anything specific. I have changed mine once (on a 33) but the bigger boats have a much bigger anode which I would guess lasts much longer.

[Ziffius]

When I bought my Bav 39 with 130s saildrive I had it professionally serviced in Titchmarsh before sailing for the med, within 2 weeks I found the anode had fallen off - the two piece type with bolt screws top and bottom. As it sits forward of the prop that was damaged by its passing. Had a diver replace the anode in Cagliari and that fell off within 2 days. So had another diver fit one in Corfu. Since then I fit my own and loctite it and check it regularly - haven’t lost one since.

[Sootydog]

Well, she is out of the water now and the anode is definately missing.  There is a very small "ding" on the leading edge of one of the prop blades. 
The saildrive leg looks fine, probably due to it being coated in several layers of anti-foul.
The surfaces of the prop look a bit worn, pitted and powdery in places.  I assume I can carefully sand the blade surfaces and re-coat with something.  Any recommendations?

[Symphony]

Hope your saildrive is not coated with normal AF which contains copper. The correct one to use is either International Trilux or Hempel Mille which are specifically for use on aluminium. Clean both housing and prop back to the original Volvo coating which is light blue/grey on the housing and usually black on the prop then use the Trilux or Mille spray - primer and topcoat following the instructions.